Rotary machines equipped with an active magnetic suspension are already known, such as for example from U.S. Pat. No. 4,180,946. The suspension of the rotary shaft of a machine by means of active magnetic bearings presents many advantages. It is however necessary to add to the magnetic bearings, auxiliary or back up bearing, generally of ball bearings type, in order to support the rotor in stop position, or in working position in case of failure of the supply to the active magnetic bearings. Said ball bearings, having a metal-with-metal contact, are subject to early wear when they are in service and do not allow a soft landing of the rotor in case of failure of the magnetic bearings. They further contribute to increasing the overall dimensions of the suspension.
It has also been proposed to support a turbo-machine with a radial active central magnetic bearing together with radial fluid end bearings, in order to combine the advantages of fluid bearings with those of magnetic bearings. This type of suspension remains however complex and cumbersome and does not provide all the advantages of the complete active magnetic suspensions with five controlled axes of the type comprising at least one axial magnetic thrust bearing and two radial magnetic bearings with their associated detectors.